Modulation of B Lymphocyte Differentiation by Calcitonin Gene-Related Peptide (CGRP)

Abstract

The presence of calcitonin gene-related peptide (CGRP) in nerve endings in lymphoid organs, around blood vessels, and in bone marrow suggests that it might influence the function and differentiation of lymphoid cells. Previous studies identified specific CGRP receptors on mature T and B lymphocytes and on 70Z/3 pre-B cells. In these studies, it was found that CGRP stimulated a rapid, prolonged elevation of cAMP with in 70Z/3 cells with an ED50 of approximately 20 fM. Following CGRP treatment, cAMP levels peaked within 5 min and were still elevated after 60 min. The effect of CGRP on surface immunoglobulin (sIg) expression was examined by treating 70Z/3 cells with CGRP, or combinations of CGRP and LPS, and then measuring slg expression by FACS. When 70Z/3 cells were treated with LPS, CGRP, or calcitonin for 48 hr, only LPS induced the expression of sIg, increasing the percentage of cells expressing sIg from less than 10% positive in untreated cells to 80-98% positive. Subsequent experiments examined the effect of CGRP on LPS-induced sIg. CGRP inhibited LPS-induced sIg expression at concentrations ranging from 10-15 to 10-7M. The maximal inhibition was observed at CGRP concentrations ranging from 10-10 to 10-8M, and the maximal reduction of sIg expression was about 40%. The inhibitory effect of CGRP was specific in that it could not be mimicked by calcitonin and could be blocked by the CGRP receptor antagonist CGRP8-37. A similar dose-dependent inhibitory effect on LPS induction was observed in 70Z/3 cells treated with LPS and dibutyryl cAMP, suggesting that the inhibitory effect of CGRP on sIg expression is mediated by stimulation of intracellular cAMP. The inhibitory effect of CGRP on LPS induction of sIg appears to be mediated by a reduction in the expression of both μ and κ mRNA. When μ and κ expression were examined by Northern blot analysis, it was found that CGRP caused a 50% reduction in the amount of μ and κ mRNA induced by LPS. The ability of CGRP to inhibit differentiation of 70Z/3 cells and sIg expression provides evidence that CGRP can influence the differentiation of lymphopoeitic precursors.